Can mouse poison harm predators that eat mice? Should we use traps instead?

By the time a predator eats a poisoned mouse, the poison will likely have been digested and won’t be as strong. To be poisoned, a mouse needs to eat enough bait to equal one-quarter to one-third of its own body weight. The same would go for a larger animal; it would need to ingest a quarter of its own weight in bait to obtain a lethal dose. Traps, however, are safer if there are children or other animals around.

You need to monitor bait stations daily when you’re using them. Once the mice have ingested a lethal dose, it can take up to two weeks for them to die, and you’ll need to keep baiting for 15 days afterwards to make sure there’s no activity. If you aren’t at the cottage frequently enough, you probably should use traps instead.